For our example, let us create a table with NOT NULL constraint. After that, we will modify a column to allow NULL. The following is the query to create a table with NOT NULL constraint. mysql> create table AllowNullDemo -> ( -> id int not null -> ); Query OK, 0 rows affected (0.48 sec)= Insert records with the help of INSERT command. The query is as follows. mysql> insert into AllowNullDemo values(); Query OK, 1 row affected, 1 warning (0.19 sec) mysql> insert into AllowNullDemo values(); ... Read More

You can enable ONLY_FULL_GROUP_BY in MySQL as shown in the following query − mysql> SET sql_mode = 'ONLY_FULL_GROUP_BY'; Query OK, 0 rows affected (0.01 sec) As shown above, we can enable ONLY_FULL_GROUP_BY with the help of SET command. To disable ONLY_FULL_GROUP_BY with the help of the following query − mysql> SET GLOBAL sql_mode=(SELECT REPLACE(@@sql_mode,'ONLY_FULL_GROUP_BY','')); Query OK, 0 rows affected (0.04 sec) We have disabled ONLY_FULL_GROUP_BY successfully.

The MySQL’s DESCRIBE or DESC both are equivalent. The DESC is the short form of DESCRIBE command and used to dipslay the information about a table like column names and constraints on column name. The DESCRIBE command is equivalent to the following command − SHOW columns from yourTableName command. The following is the query that display information about a table with the help of DESCRIBE command. The query is as follows. mysql> DESCRIBE Student; Above, Student is the table name in my database. The above query generates the following output. +-------+--------------+------+-----+---------+-------+ | Field | Type ... Read More

To get the list of MySQL user accounts, we can use “SELECT USER”. The following is the query to display the list. SELECT User FROM mysql.user; Here is the output. +------------------+ | User | +------------------+ | John | | Mac | | Manish | | mysql.infoschema | | mysql.session ... Read More

We can return 0 for NULL in MySQL with the help of IFNULL() method. The syntax of IFNULL() is as follows. IFNULL(YOUREXPRESSION, 0); Let us see an example. First, we will create a table. mysql> create table NullDemoWithZero -> ( -> id varchar(200) -> ); Query OK, 0 rows affected (0.65 sec) After creating a table, let us insert some records in the table using the INSERT command. The query is as follows − mysql> insert into NullDemoWithZero values(); Query OK, 1 row affected (0.16 sec) ... Read More

The int type takes 4 byte signed integer i.e. 32 bits ( 232 values can be stored). The BigInt type takes 8 byte signed integer i.e. 64 bits (264 values can be stored). Let us see an example. Creating a table with zerofill, that would add leading zeros. mysql> create table IntandBigint20Demo -> ( -> Number int(20) zerofill, -> Code BigInt(20) zerofill -> ); Query OK, 0 rows affected (0.58 sec) After creating a table, we will insert records into the table. mysql> insert into ... Read More

Let’s say we have a table and now there is a requirement to add AUTO_INCREMENT on column name. For that, use the MODIFY command. Here, we will create a demo table first. mysql> create table AddingAutoIncrement -> ( -> Id int, -> Name varchar(200), -> Primary key(Id) -> ); Query OK, 0 rows affected (0.47 sec) We have created a table above and now let us alter the table to add AUTO_INCREMENT on column name ‘Id’. The syntax is as follows − ... Read More

First, let us create a table with the UNIQUE constraint. It suggests that we cannot add duplicate values. Creating a table. mysql> create table UniqueConstraintDemo -> ( -> Name varchar(200) unique -> ); Query OK, 0 rows affected (1.05 sec) Now, we can check whether the table has UNIQUE constraint or not with the help of DESC command. The query is as follows. mysql> DESC UniqueConstraintDemo; The following is the output. +-------+--------------+------+-----+---------+-------+ | Field | Type | Null ... Read More

To add composite primary key, use the ALTER command. Let us first create a demo table The query to create a table. mysql> create table CompositePrimaryKey -> ( -> Id int, -> StudentName varchar(100), -> Age int -> ); Query OK, 0 rows affected (0.56 sec) Haven’t added composite primary key above till now. Let us now check with the help of desc command. mysql> desc CompositePrimaryKey; The following is the output. +-------------+--------------+------+-----+---------+-------+ | Field ... Read More

The replace() function can be used to replace a string with another string. To understand replace(), we need to create a table with some records. The following is the query to create a table. mysql> create table replaceDemo -> ( -> Name varchar(200) -> ); Query OK, 0 rows affected (0.55 sec) Insert some records with the help of INSERT command. The query to insert records is as follows − mysql> insert into replaceDemo values('John'); Query OK, 1 row affected (0.17 sec) mysql> insert into replaceDemo values('Demo'); ... Read More